The aim of this study was to investigate empirically the extent of mandatory compliance with international accounting standards (IASs) by companies in the Gulf Co-Operation Council (GCC) member states - namely, Bahrain, Oman, Kuwait, Qatar, Saudi Arabia and the United Arab Emirates (UAE) - between 1996 and 2002, and to explain why some companies comply more than others. Official personnel in the relevant enforcement bodies were interviewed to obtain information about their monitoring and enforcement activities. An index of compliance was devised to quantify the level of compliance. This was applied to the financial statements of 137 listed companies. Multivariate regression analysis was employed to explore the relationships between the level of compliance and particular attributes of the companies and year-by-year dummy variables. This was done to discover if the level of compliance with IASs was influenced only by company attributes or whether there were time trends as well. The attributes were country of origin, size, leverage, liquidity, profitability, auditor, industry, internationality, ownership diffusion and the company’s age. The average level of compliance for all companies and all years was 75% of the items in the index. No company within the examined time period fully complied with all requirements. The average level of compliance increased over time, though, from 68% in 1996 to 82% in 2002. There was significant variation in the level of compliance across the six GCC member states as well, but the level of compliance increased in all states over the sample period. The highest average level of compliance was in Saudi Arabia, where it reached 88% in the last year of the study. The degree of non-compliance with IASs across the GCC member states was partially attributable to limited monitoring and enforcement by the bodies responsible for overseeing financial reporting, and to the limited comprehensiveness of audits by external auditors. In addition to the role of the enforcement bodies and external auditors, several company attributes helped explain the level of compliance with IASs. Compliance variation increased with a company’s size, leverage and internationality. The level of compliance varied by industry too; however, company profitability, liquidity, ownership diffusion and whether the audit was conducted by a major international audit firm were found not to be significant factors.